Throughout this application, various publications are referenced and citations provided for them. Some of the references are referred to by arabic numerals within parenthesis. Full bibliographic citations for these references are provided in the specification immediately preceding the claims. The disclosure of these publications in their entireties are hereby incorporated by reference into this application to more fully describe the state of the art to which this invention pertains.
Much of the disclosure of U.S. application Ser. No. 844,864, filed Mar. 27, 1986 has been published. See, e.g., Kim et al., Cancer Letters, vol. 31, pp. 69-76, 1986.
Exposure of mammalian cells to ionizing radiation results in the production of potentially lethal damage (PLD), the repair of which depends on the proper post-irradiation condition under which cells are held. See, e.g., Phillips et al, Radiat. Res. 29: 414 (1966); Hahn et al, Curr. Top Radiat. Res. Q. 8 39 (1972). The post-irradiation exposure of irradiated cells to restrictive conditions where they cannot enter the first semi-conservative DNA replication after irradiation results in enhanced radiation induced cell killing, as has been shown by Iliakis, et al., Int. J. Radiat. Biol. 42:417 (1982). Such conditions are frequently found in the microenvironment of large solid tumors, which are usually characterized by low pH, low oxygen tension and a nutritionally deficient state. The possible importance of PLD repair in tumor control by radiation has recently received attention following cell culture studies that have demonstrated a correlation between radiocurability of human tumors and their capacity for PLD repair in vitro. Weichselbaum, et al., Radiation Biology in Cancer Research, p. 345 et. seq. (Raven Press, 1980); Weichselbaum et al, Brit. J. Cancer 46: 532 (1982).
The classes of agents reported to inhibit the repair of PLD in cell culture systems are inhibitors of DNA synthesis and of energy metabolism. Iliakis, Radiat. Res, 82: 537 (1980); Nakatsugawa et al, Int. J. Radiat. Biol., 41: 343 (1982); Hahn, et al, Brit. J. Cancer 50:657 (1984). Among the inhibitors of DNA synthesis, .beta.-arabinofuranosyl adenine (.beta.-ara-A), an anti-viral agent, was shown to be a potent inhibitor of PLD repair. However, when .beta.-ara-A was tested for its radiation potentiating effects on an in vivo murine tumor, the study failed to show any potentiation of radiation effects. Nakatsugawa, Modification of Radiosensitivity in Cancer Treatment, p.221 (Acad. Press, 1984). The reason for the negative result of .beta.-ara-A may be related to the fact that .beta.-ara-A is readily inactivated by hydrolysis to arabinofuranosyl hypoxanthine via adenosine deaminase. An alternative approach to potentiating the anti-viral and anti-neoplastic activity of .beta.-ara-A is to use an analog which is not inactivated by adenosine deaminase. 2-fluoro-arabinofuranosyl adenosine monophosphate (fludarabine phosphate) the first phosphorylated metabolite of 2-fluoro-ara-A, has been shown to inhibit DNA polymerase and ribonucleotide reductase in vitro. Brockman et al, Biochem. Pharmacol. 26:2193 (1977); White et al, Proc. Am. Assoc. Cancer Res., 27:33 (1981).
Fludarabine phosphate is a synthetic analog of .beta.-arabinofuranosyl adenine, which has been found not to be inactivated by adenosine deaminase, unlike .beta.-ara-A. In view of the fact the .beta.-ara-A was useful as a PLD inhibitor in vitro, but in vivo tests proved negative, fludarabine phosphate was used as a potential inhibitor of potentially lethal damage in radiotherapy in vivo. The results obtained, using this compound, show that fludarabine phosphate is a useful therapeutic agent in radiotherapy.